6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum

TWANG · Post by **TWANG** » Sun 11/21/10 5:53 pm

I think that's the same drill plan I printed out.
and I couldn't size it to match my board at all. even going by tenths of a percent.
that does look like the right schematic though..

I'm not worried about the drill plan.. two tube mounts on the board have center holes..
I may even drill a small hole in the other two, but I don't really need to.

I'll put standoffs on the board.. use a fine sharpy around each standoff..
stick a mark through the tube holes.. mark the outside edges of the others.

What I really could have used was an idea of how far out from the panel to put it.. how far away the transformers should be..
But I'll just go by the Baby Will... should be close enough.
I always worry there's some secret or detail that would make it better I wont catch until later.

I cleaned the shop and found about a hundred standoffs in three lengths.
That place was a pit!

I am concerned about the build though. those drawings and instructions I only save the urls for.. all gone!

xlch · Post by **xlch** » Sun 11/21/10 6:34 pm

I would take it to print shop and have them print it to size but thats just me. I was concerned to but thats also why I downloaded all of the files and saved them in a couple of different locations so I dont lose them.
I have all of my parts for the Baby Will ordered but the transformers and figuring out what method of rectification I want to use. The chassis and tubes will be here after the holiday. I also had to contact AES because the two Cliff Jacks that are part of the Scratch Build Kit were missing. Im not to worried about it though I am sure they will make it right.
I made a nice score the other day a friend of mine gave me a bunch of different preamp tubes. There were 5 JJ ECC83s 4 EH 12ax7s, 4 Mesa 12ax7s and a couple of Groove Tube Chinese 12ax7s . All of them are only a couple of months old and most of them were only used for about a week or two. I dont think I am going to have to buy any preamp tubes for awhile.

Post by **rock_mumbles** » Sun 11/21/10 11:00 pm

xlch wrote:Twang
This should be the Drill plan you need
http://rh-tech.org/public/z_stingray_pc ... n%20v1.pdf
If this is not correct your going to have to use your PCB to mark the holes out and drill to the correct size. I do have a couple of the PCBs here that I have not started on. I dont own a scanner but I can have them scans of both sides made if it will help people out.
The schematic shows how to wire up the transformers.
Here
http://rh-tech.org/public/z_stingray_pc ... c%20v3.pdf

If you have one of the bare Superlite II v2.7 pcb it would be really nice to have both sides scanned at 300 dpi ... so from that we can figure out build questions.

If you could email them to me I'll put them on my site ...
email me at: rollie (AT) isp DOT com

TWANG · Post by **TWANG** » Mon 11/22/10 12:40 am

I only have about half the parts in.. I suppose I could take them out and get it over to a print shop.
I'll give it a go. people are gonna need 'em and maybe someone will make 'em again or a point to point version.

xlch · Post by **xlch** » Mon 11/22/10 5:16 pm

Rock
I just sent you the scans I made of the SuperLite II. Let me know if they are not what you were looking for and I will gladly scan them off again.

StarGeezers · Post by **StarGeezers** » Thu 11/25/10 10:29 am

Sorry, not to get too off topic here, I'd like to report a Trouble with my Ab Min ...

Yes, after all this time , it's suddenly experienced a loss of Gain

... Investigating Now ... PI tube is suspect ... I Dunno' !!! ZP approved/improved the PI , so I'd expect all's well there ... maybe just a weak tube ... I realize they don't last forever, especially the newer ones ... grrrrr!!!!

I have "heard" the PI tube is the hardest working tube in the amp ... I can't think why if properly set up...??? Must consult the "Masters"...

Dustpuppy · Post by **Dustpuppy** » Thu 11/25/10 1:10 pm

Sorry to hear that Geez, mine is still running strong (loud) *crossed fingers*

I was experimenting with the schematic this week and tried building it with dual 6sj7 preamp gain stages. Started out with oscillation at 12 o'clock on master and gain. After some tapping and swapping of tubes, I discovered a microphonic tube in the second preamp stage. Again I used a 1000 uF cathode bypass on the power tubes to tighten bass. This thing has ludicrous gain. I added a 470k grid leak on the second pre stage and didn't cut much. I'd say 2 6sj7 with this PI is definitely overkill.
As Merlin's book suggests that pentodes work better with a gain stage pushing them, I'm working on a schematic with a dual triode split for the 1st and 3rd pre stage with the 6sj7 between them. Any idea what I should use on the PI cathode to lower the gain a tad? Or a mid MU dual triode?
Let me know if you want me to start a new thread as I seem to be drifting off topic.

Brett

Post by **zaphod_phil** » Thu 11/25/10 5:27 pm

Don't try to limit the gain of the PI, as you need that in order to drive the power tubes. You just need to use a pair of resistors as a divider to attenuate the signal between your 6SJ7 and the PI. Or if you want to go with a multi-stage preamp, then you also need to do that between each stage. The idea is not to drive the grids of each stage too hard.

insanecopilot · Post by **insanecopilot** » Thu 11/25/10 6:50 pm

Dustpuppy wrote:Sorry to hear that Geez, mine is still running strong (loud) *crossed fingers*

I was experimenting with the schematic this week and tried building it with dual 6sj7 preamp gain stages. Started out with oscillation at 12 o'clock on master and gain. After some tapping and swapping of tubes, I discovered a microphonic tube in the second preamp stage. Again I used a 1000 uF cathode bypass on the power tubes to tighten bass. This thing has ludicrous gain. I added a 470k grid leak on the second pre stage and didn't cut much. I'd say 2 6sj7 with this PI is definitely overkill.
As Merlin's book suggests that pentodes work better with a gain stage pushing them, I'm working on a schematic with a dual triode split for the 1st and 3rd pre stage with the 6sj7 between them. Any idea what I should use on the PI cathode to lower the gain a tad? Or a mid MU dual triode?
Let me know if you want me to start a new thread as I seem to be drifting off topic.

Brett

Glad to see someone has built a double 6sj7 18watt. I have been wanting to do the same after building a couple of double 6sj7 SE amps. I would imagine you would have a lot of gain

Dustpuppy · Post by **Dustpuppy** » Thu 11/25/10 8:51 pm

zaphod_phil wrote:Don't try to limit the gain of the PI, as you need that in order to drive the power tubes. You just need to use a pair of resistors as a divider to attenuate the signal between your 6SJ7 and the PI. Or if you want to go with a multi-stage preamp, then you also need to do that between each stage. The idea is not to drive the grids of each stage too hard.

Do I need the voltage divider or can I just run a grid leak to ground to drop some of the incoming signal?

I left Merlin's book at work this weekend, if I did a divider on the PI, would it go before or after the grid stopper?

StarGeezers · Post by **StarGeezers** » Fri 11/26/10 8:16 am

Got mine fixed, weak PI tube ...??? I guess ... swapped a new one in and it was much better ...
I've been using the Ab Min all along with the RF Drive up front ... (poor man's channel switching ) ... That drives the Big Red (5693) pretty well ...

Guys , I play mostly with Cleans, so the simple Ab Min works fine for me ... I just turn it up as loud as it needs to be , and add the dirt with the RFD... great for my "oldies" gigs ... Without the RFD it will still go into the dirty Blues zone .. when cranked , but it does get LOUD !!

Latest idea is to rewire the PI fils to accommodate the 6N2Pev ... which I have a lot of , and they're CHEAP and sound Good !!! Used one for the Dog Sled PI ... works Fine !!!

As Echuta so aptly stated .. " We're cheap bastards ! "

Post by **zaphod_phil** » Fri 11/26/10 6:23 pm

Guys , I play mostly with Cleans...

You really need to try and get out some more!

StarGeezers · Post by **StarGeezers** » Sat 11/27/10 9:45 am

ZP, when you get as old as me

, they actually let you play with Cleans ....

But alas , I LOVE a bit of Dirt too ... Nice contrast for the Cleans ... Just the old crap we play , not much call for it

TWANG · Post by **TWANG** » Sat 11/27/10 5:46 pm

Got my parts for the superlite II 2.7 in so I'll start that over the course of the next week.

But no doubt about it.. AbMin in a vj chassis for sure.

I'm conflexed (hey if s palin can make up words, I can too)
though..
about what tubes I oughta go for.

I do have an awuful lot of el84 builds..and a couple of el34s.. so..
push me around, I can take it.

mcrracer · Post by **mcrracer** » Sat 11/27/10 5:56 pm

Ab Min with 6V6s, 5693 (RED!!!) and a 12AX7 PI

TWANG · Post by **TWANG** » Sat 11/27/10 6:25 pm

OK. sold.
I've got a pair of JJ 6V6s and no amp for 'em so. that's perfect.

Dustpuppy · Post by **Dustpuppy** » Sat 11/27/10 6:29 pm

Hard to beat REAL 6v6's in an Ab Min. Ditch the JJ's and pick up a pair of Sylvania or RCA. Same price or less and better sound.

StarGeezers · Post by **StarGeezers** » Sun 11/28/10 11:17 am

Good tubes always make the difference eh !!!

StarGeezers · Post by **StarGeezers** » Sun 11/28/10 2:38 pm

Good News !!! I removed That Tone Control from my Ab Min and now it's REALLY LOUD !!!

Just a Volume and the tweed TC ... Perfect !!!

TTC was a nice option with the mid sweeps , just too "lossy" ...

insanecopilot · Post by **insanecopilot** » Sun 11/28/10 3:54 pm

Never tried "that tone control" heard it was real lossy. I like the tweed with 6v6's and the 18watt tone control with el84's. The tweed works real fine in my 6sj7/6v6 18watt. Have you tried any of BigBeck's single knob experiments?

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6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum